1. Field of the Invention
The present invention relates to an error correction apparatus in a digital communication system using a BCH (Bose-Chandhuri-Hocqueghem) code, more particularly relates to a BCH code decoding apparatus for correcting a complex error in a digital communication system.
2. Description of the Prior Art
FIG. 1 is a block diagram showing a conventional combined-error-correcting circuit for correcting both random and burst errors, as described, for example, in "Error Control Coding: Fundamentals and Applications" by S. LIN and D. J. COSTELLO, Jr., pp. 280-282, published by Prentice-Hall, Inc., 1988. In the figure, numeral 1 is an input terminal for inputting a received coded message, 39 is a burst-error-correcting unit for correcting a burst error by burst trapping, 40 is a random-error-correcting unit for correcting a random error, 6 is an output selecting circuit for selecting either the output from the burst-error-correcting unit 39 or the output from the random-error-correcting unit 40 and 9 is an output terminal for outputting an decoded result.
The operation of the above-mentioned prior art will now be described. A received message which has been decoded at a transmitter site before transmitting and includes errors added in the communication path is input from the input terminal 1 into both the burst-error-correcting unit 39 and the random-error-correcting unit 40. The message is decoded by the respective correcting units, and either the decoded output from the burst-error-correcting unit 39 or the decoded output from the random-error-correcting unit 40 is selected by the output selecting circuit 6 in response to the condition of the communication path, and thereby the selected output is delivered from the output terminal 9 as an output of the complex error correcting circuit.
Since conventional complex error correcting circuits are generally arranged as described above, it is necessary to control the output selecting circuit 6 in response to the condition of the communication path with respect to the concrete error correcting code, but there is shown no definite suggestion as to how the condition of the communication path can be concretely grasped and there is also shown no criterion to appropriately judge such a condition, therefore it is difficult to accurately control the selecting circuit 6. There is a further problem that, because of the burst error correcting unit and the random error correcting unit being independently arranged from each other, it is necessary that the respective units independently include syndrome generating circuits for extracting the error condition.